An conventional ESD-protective-function-equipped composite electronic component 500 illustrated in FIG. 12 and FIG. 13 includes a thin-film capacitor 505 that includes a first capacitor electrode layer 502 stacked on an insulating substrate 501, a dielectric layer 503 stacked on the first capacitor electrode layer 502, and a second capacitor electrode layer 504 stacked on the dielectric layer 503. In addition, the ESD-protective-function-equipped thin-film capacitor 500 includes a protection circuit 506 that is connected in parallel to the thin-film capacitor 505. It is noted that FIG. 12 is a plan view illustrating an ESD-protective-function-equipped composite electronic component of the related art, and FIG. 13 is a cross-sectional view taken along line A-A of FIG. 12.
The protection circuit 506 is formed of a plurality of (six) Schottky diodes 507a to 507f each having a thin-film structure, the Schottky diodes 507a to 507f being connected in series. For example, each of the Schottky diodes 507a to 507f included in the protection circuit 506 is formed in the following manner. That is to say, an electrode 508a is formed on a circumferential edge portion of the dielectric layer 503 so as to have a frame-like shape. The electrode 508a is connected to the first capacitor electrode layer 502 formed in a substantially rectangular shape.
As illustrated in FIG. 12, the second capacitor electrode layer 504 first formed in a substantially rectangular shape and then a lower right corner portion thereof with a substantially elongated rectangular shape has been cut away. Electrodes 508c and 508e each having a rectangular shape are formed on a portion of the dielectric layer 503, the portion being located at a position corresponding to the lower right corner portion of the second capacitor electrode layer 504, which has been cut away. A semiconductor layer 509 is formed on the dielectric layer 503 so as to partially coat the electrodes 508a, 508c, and 508e. When viewed in plan view, an electrode 508b is formed on the semiconductor layer 509 so as to be located between the electrode 508a and the electrode 508c, and an electrode 508d is formed on the semiconductor layer 509 so as to be located between the electrode 508c and the electrode 508e. The electrode 508f is formed on the semiconductor layer 509 so as to be located between the electrode 508e and the second capacitor electrode layer 504.
Accordingly, the Schottky diode 507a is formed of the electrodes 508a and 508b and the semiconductor layer 509. The Schottky diode 507b is formed of the electrodes 508b and 508c and the semiconductor layer 509. The Schottky diode 507c is formed of the electrodes 508c and 508d and the semiconductor layer 509. The Schottky diode 507d is formed of the electrodes 508d and 508e and the semiconductor layer 509. The Schottky diode 507e is formed of the electrodes 508e and 508f and the semiconductor layer 509. The Schottky diode 507f is formed of the electrode 508f, the second capacitor electrode layer 504, and the semiconductor layer 509. The protection circuit 506 is formed of the Schottky diodes 507a to 507f, which are connected in series. The electrode 508a of the Schottky diode 507a is connected to the first capacitor electrode layer 502, and as a result of one of the electrodes of the Schottky diode 507f being formed of the second capacitor electrode layer 504, the protection circuit 506 is connected in parallel to the thin-film capacitor 505.
In the ESD-protective-function-equipped composite electronic component 500, as described above, when an overvoltage caused by static electricity or the like is applied to the thin-film capacitor 505, the Schottky diodes 507a to 507f, which form the protection circuit 506, break down, and a current path is formed in the protection circuit 506. Thus, the thin-film capacitor 505 is protected as a result of an overcurrent flowing through the protection circuit 506. It is noted that each of the Schottky diodes 507a to 507f has a metal-semiconductor-metal structure and is formed so as to serve as an antiparallel Schottky diode in which the flow of current is limited by tunneling through a Schottky-junction metal-semiconductor Schottky barrier. The dielectric layer 503 is composed of stoichiometric silicon nitride (Si3N4), silicon dioxide (SiO2), or the like. The semiconductor layer 509 is composed of silicon-rich non-stoichiometric silicon nitride, tantalum pentoxide (Ta2O5), or the like.
Patent Document 1: Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2002-541681.
As described above, in the ESD-protective-function-equipped composite electronic component 500, the protection circuit 506 is formed by connecting in series the Schottky diodes 507a to 507f, each of which has a Schottky-junction metal-semiconductor-metal thin-film structure. Since the electrical barrier height of a Schottky barrier is theoretically about 2 eV or less, the voltage at which a current sharply increases is about 2 V or less. Consequently, in the case where the working voltage of the thin-film capacitor 505 is 2 V or more, if only one Schottky diode is connected in parallel to the thin-film capacitor 505, the current flows through the path on the Schottky diode side, and thus, the thin-film capacitor 505 cannot function.
Therefore, as described above, in the ESD-protective-function-equipped composite electronic component 500, the voltage value, at which the current increases, is increased by connecting in series the plurality of Schottky diodes 507a to 507f, so that the functions of the thin-film capacitor 505 are ensured. However, in this configuration, the number of the Schottky diodes 507a to 507f, which are connected in series, increases, and thus, there is a problem in that the element size of the ESD-protective-function-equipped composite electronic component 500 increases.